The latest deployment comes as the aircraft carrier battle group the USS Constellation set sail for the Gulf from San Diego, California this past weekend.

The cargo vessels, the USNS Bellatrix, the USNS Bob Hope and the USNS Fisher, just short of the length of aircraft carriers themselves, are some of the largest transport ships in the U.S. military's inventory.

Marge Holtz, director of the Military Sealift Command (MSC), a branch of the U.S. Navy charged with running the ships on behalf of the U.S. armed forces, declined comment on the exact destination of the vessels.

"It is part of the repositioning of forces and equipment in support of the war on terror. They are on route," she told Reuters from Washington.

Two, the USNS Fisher and USNS Bob Hope, have seven decks capable of carrying tanks, helicopters and other heavy armor MSC says.

Over 900 feet long and 100 feet wide each has a hold capacity of 380,000 square feet -- equivalent to eight soccer fields.

According to MSC the vessels are capable of carrying 58 Abrams battle tanks, 48 track vehicles, such as armored vehicles, and 900 other trucks.

Holtz said the ships would also carry "tanker trucks and bridge sections."

Eight of their sister ships, known as the Watson-class, and similarly packed with armor and supplies for the U.S. Army, are anchored around the British base of Diego Garcia in the Indian Ocean, within a few days sail of the Gulf.

The fast sealift ship the USNS Bellatrix, of a similar size but quicker -- it is one of the fastest cargo ships in the world -- loaded equipment for the U.S. Marine Corps on the west coast of the United States and set sail last week.

The two others, Large Medium Speed Roll-on Roll-off (LMSR) ships, had loaded equipment for mechanized U.S. army units on the east coast and set sail in the last 14 days. "One last week and one the week before," Holtz said.

There are another six fast sealift ships and seven LMSRs berthed at U.S. ports awaiting orders according to the MSC.

In addition to these government-owned ships the Department of Defense (news - web sites) has regularly chartered merchant vessels to carry tanks, ammunition, helicopters and other supplies to the Gulf.

Since August the Pentagon has chartered at least eight large vessels.

On Friday MSC confirmed to Reuters it had chartered two ships to move a massive quantity of ammunition and a smaller quantity of armor to the Gulf and the Red Sea.